1. Field of the Invention
The present invention relates to a frame interpolation method and apparatus of interposing at least one interpolation frame between adjacent frames for the purpose of decreasing a display frame interval in playing back a video image, and an image display system using the same.
2. Description of the Related Art
In a hold model picture display apparatus which continues to display a previous frame till an image is newly written in, such as a liquid crystal display and an electroluminescence display, there are problems such as a blurring occurring when eyes of a viewer follow movement of a moving object in a video display, and an unnatural movement due to displaying a video with a few frames.
A display frame interval may be decreased for the problems to be solved. A concrete method of decreasing a display frame interval is to generate an interpolation frame using motion compensation used by MPEG (Motion Picture Experts Group) and to interpose it between adjacent frames. In the motion compensation in MPEG, a motion vector detected by an image block matching method is used. The image block matching method includes dividing a first reference frame into a plurality of first image block, searching a second reference frame approximate to the first reference frame for a second image block having a maximum correlation with respect to each first image block, and deriving a motion vector from the second image block to the first image block.
In the image block based frame interpolation method using such motion compensation, when an interpolation frame is generated by the motion compensation, at first a scaling process which converts a first motion vector between the first and the second reference frames to a second motion vector between the interpolation frame and the first reference frame is carried out. Carrying out the motion compensation using the second motion vector provided by the scaling process generates the interpolation frame. In other words, the end point of the second motion vector is fixed on the first reference frame, and the image data of the image block indicated by the end point of the second motion vector is copied to the position of the to-be-interpolated block indicated by the starting point of the second motion vector on the interpolation frame.
In this method, the starting point of the second motion vector provided by the scaling does not always coincide with the position of the original to-be-interpolated block on the interpolation frame. For this reason, a gap having no image data or a region on which image data are overlapped may occur on the interpolation frame.
Japanese patent publication No. 2528103 (patent document 1) discloses a frame interpolation method without such a gap or overlapping. This method interpolates a frame by deriving correlation between reference frames located before and after with respect to a to-be-interpolated block on the interpolation frame. As a result, it is possible to generate an interpolation frame directly by using the motion vector derived at first without scaling of a motion vector. Further, the to-be-interpolated blocks are arranged on the interpolation frame in a form of a uniform lattice, so that the gap or overlapping does not occur on the interpolation frame.
The method of the patent document 1 is an image block based method to process an image in units of an image block similarly to MPEG. For this reason, there is a problem that a block distortion occurs on a boundary between the image blocks on the interpolation frame in the case that there are a plurality of movements in the image block.
When an object moves from left to right on a stationary background, interpolation is performed on the background around the object. In this time, completely different backgrounds are averaged, resulting in producing a different background around the object. Therefore, a gap occurs between the background around the object and the original background on the outside thereof. The gap is visually recognized as block distortion.
An object of the invention is to provide a frame interpolation method and apparatus wherein no block-to-block gap and no block overlapping occur on an interpolation frame and block distortion is suppressed, and an image display system using the same.